The present invention relates to a steering valve device to correct a deviation between a steering wheel and steered wheels of a motor vehicle.
A power steering device 90 arranged to assist in the turning of steered wheels 34 in response to the rotational operation of steering wheel 4 ,as shown in FIG. 4, is known in the art. The power steering device 90, which includes a hydraulic control circuit in which there are a hydraulic source such as a pump 2 and a tank 21, a power steering valve 91 connected to the source, and a power steering cylinder (hereinafter a PS cylinder) 3 connected to the valve 91 by means of hoses 911, 912, operates to turn steered wheels 34 left and right. In response to rotational operation of the steering wheel 4, the steering valve 91 distributes fluid from the source to either a right or left chamber of the PS cylinder 3 and returns fluid from the other chamber to the source according to the rotational direction 41 of the steering wheel 4. The PS cylinder then turns the steered wheels 34 in the direction 31 corresponding to the fluid distribution.
The steering wheel 4 has a knob 43 thereon by which an operator can ascertain the steering angle of the wheel 4 reflecting the angle of the steered wheels 34. However, there is a situation when the knob 43 incorrectly indicates the angle of the steered wheels 34; that being when there is a deviation in the relative angular positions of steering wheel 4 and steered wheels 34 due to a leakage of hydraulic fluid from the circuit. To replenish the hydraulic fluid, the hydraulic circuit further includes a correction valve 92 between the steering valve 91 and the PS cylinder 3. The correction valve 92 shortens the hoses 911, 912, as discussed in Japanese Examined Patent Publication Nos. 3-30544 and 4-24270 and Japanese Examined Utility Model Publication No. 7-5364. A controller 5 and sensors 32, 42 are further provided for detecting angles of the steered wheel 34 and the steering wheel 4, respectively. The controller 5 controls the valve 92 to be open and close based on signals from the sensors 32, 42 indicating whether there is a deviation in the position relation between the steering wheel 4 and the steered wheels 34. Accordingly, the knob position of the steering wheel 4 is corrected by the opening and closing control of the correction valve 92.
However, the conventional power steering device 90 has the several disadvantages. First, the power steering valve 91 and the correction valve 92 are arranged in the respective housings 93, 94 that are disposed away from each other. This layout is inconvenient because separate parts have to be placed in the limited space. Second, piping, such as a hose, is needed between the power steering valve 91 and the correction valve 92. The inclusion of such piping increases manufacturing costs and assembling time.
It is an object of the present invention to provide a steering valve device for reducing both the space necessary for the device in the vehicle, and the costs and time for manufacturing the device.
A steering valve device of the present invention comprises a main valve having a supply port to which hydraulic fluid is supplied from a hydraulic source, a drain port from which the fluid is drained to the source, and a pair of right and left outlets either of which allows the fluid to flow into the cylinder and the other of which allows to receive the fluid from the cylinder, the main valve being operable in response to an operation of the steering wheel, a communicating passage for communicating the right outlet with the left outlet, a correction valve for opening and closing the communicating passage, and a housing in which the main valve, the communicating passage, and the correction valve are arranged.
The most remarkable point of the present invention is that the main valve, the communicating passage and the correction valve are arranged together in the housing.
The operation and effect of the present invention will now be explained.
As mentioned above, the steering valve device has a housing containing both the main valve and the correction valve. Therefore, the steering valve device not only controls supply and drain of the hydraulic fluid acting on the PS cylinder by means of the main valve, but also opens the communicating passage by means of the correction valve, so that it can resolve the bias of the oil volume between the right and left outlets.
Unlike the conventional device, the steering valve device of the present invention requires no hose connection between the main valve and the correction valve. It is apparent not only that a fluid leakage between the main and correction valve rarely occurs, but that assembling the device into the vehicle is less complicated. Thus, it can reduce both space for the valve assembly in the vehicle, and the costs and time for manufacturing the device.
Furthermore, the housing may comprise a first housing accommodating the main valve and a second housing accommodating the correction valve while the first and second housings are detachably fastened to each other. This invention provides easy machining of the communicating passage in the housing and maintenance of the device.